Optical instrument

ABSTRACT

An optical instrument for measuring the specific gravity of a solution, particularly the specific gravity of the acid in a lead acid battery, which incudes a base part and a transparent member, the transparent member including an incident light surface and reflector. The instrument further includes a light source arranged in the base part of the transparent member which is capable of radiating a straight-lined ray into the transparent member parallel to the axis of the member, and a photosensitive element for receiving light reflected by the incident light surface and the reflector. During use the instrument is positioned such that the transparent member is in contact with the solution whose specific gravity is to be measured.

CROSS REFERENCE TO RELATED APPLICATIIONS

This application is a continuation-in-part application of applicationSer. No. 967,985 filed Dec. 11, 1978, now abandoned, which in turn was acontinuation-in-part application of application Ser. No. 804,298, filedJune 1, 1977, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical instruments for measuring thedensity of a solution.

2. Description of the Prior Art

Refractometers for measuring the refractive indexes of liquids, such as,for example, Abbe-type or Pulfrich-type refractometers, are well known.When using such refractometers, one surface of a transparent memberhaving a known refractive index is brought into contact with a solutionto be examined a light is directed towards the surface of thetransparent member and its angle of refraction is measured to determinethe refractive index. However, these refractometers are not entirelysatisfactory since the steps for their use are complicated, involvingcollecting a fixed amount of the solution to be examined, maintainingthe solution stationary and calculating the index. In addition, when therefractive index of the solution varies with time or is converted to anelectric signal which is detected by remote control, accuratemeasurement of the index can be very difficult.

Another known apparatus for measuring the density of liquids bydetermining the refractive index is disclosed in U.S. Pat. No. 3,977,790to Schweizer et al. The apparatus utilizes a divergent light rayradiated from a light source into a light-conductive rod, the light raybeing non-parallel with the longitudinal axis of the light-conductiverod. When the divergent ray reaches a measuring or incident surface ofthe rod, the light ray is diffused so as to utilize the total reflectionangle on the measuring surface. Therefore, the fact that the light rayis non-parallel with the axis of the rod is advantageous since the lightray can be applied to the measuring surface in a wide range.

An object of the present invention is to eliminate the above-mentionedproblems with conventional refractometers.

Another object of the present invention is to provide an opticalinstrument wherein an accurate measurement of the specific gravity of asolution can be obtained by a relatively easy operation.

Yet another object of the present invention is to provide an opticalinstrument which is simple in structure and low in cost.

A further object of the present invention is to provide an opticalinstrument adaptable to a variety of uses.

SUMMARY OF THE INVENTION

In its broader aspects, the present invention comprehends an opticalinstrument for measuring the specific gravity of a solution whichcomprises an elongated transparent member, a photosensitive element anda light emitting element located at one end of the transparent member torespectively receive or send light through the transparent member, anincident light surface located at the opposite end of the transparentmember and oriented so as to be inclined with respect to the incidentrays of light directed thereagainst from the light-emitting element, anda reflector surface located adjacent to the incident light surface andoriented so as to be capable of reflecting the reflected light from theincident light surface to the photosensitive element in parallel withthe light emitted from the light source. In operation the opticalinstrument is immersed in the solution whose specific gravity is to bemeasured such that the external surface of the incident light surface isin contact with the solution, the light incident thereon being dividedinto a light portion which enters the solution and a light portion whichis reflected towards the reflector surface, this reflected light beingthen 100% reflected towards the photosensitive element to allow for adetermination of the specific graivty of the solution from the receivedlight flux.

The present invention will be more easily understood by referring to thefollowing drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show explanatory views of embodiments of opticalinstruments according to the present invention,

FIG. 2 shows a drawing which explains the principle of the opticalinstrument of the present invention,

FIG. 3 shows interrelation curves of incident light angles, reflectedlight fluxes and specific gravities of sulfuric acid,

FIG. 4 depicts the measuring principle of a conventional opticalinstrument, i.e., as described in U.S. Pat. No. 3,977,790 to Schweizeret al,

FIG. 5 shows a further embodiment of optical instrument according to thepresent invention,

FIG. 6 depicts another embodiment of optical instrument according to thepresent invention, and

FIG. 7 shows a still further embodiment of optical instrument accordingto the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1A, which shows a first embodiment of optical instrumentaccording to the present invention, the instrument body consists of atransparent glass member 1 and an elongated base part 2 made of asynthetic resin, the glass member 1 having an incident light interface1a and a reflective interface 1b at the tip which together enclose anangle of about 90 degrees, a mirror 3 being fitted to the reflectiveinterface 1b so as to reflect 100% of the light striking its surface.The incident light interface 1a and the reflective interface 1b eachhave flat surfaces. The mirror 3 is formed by securing a film of, e.g.,aluminum, silver or gold to the glass member by vapor deposition. Alight source 4 consisting of a light-emitting diode or the like islocated in the upper portion of the elongated base part 2 so as to emit,when activated by electric power fed from an electric power source (notillustrated), light towards incident light interface 1a. Further, aphotosensitive element 5 consisting of a phototransistor is arranged inparallel with the light source 4 in the upper portion of the base part2. Light from the light source 4 may be partly reflected by the incidentlight interface 1a and may reach the reflective interface 1b, andfurther the light reflected by this interface 1b may be directed inparallel with the light directed toward the incident light interface 1a.Also, it is a requirement that the light should have as little expansionas possible so that an accurate measurement may be possible. In thedrawing, a first through-hole 6 in the base part 2 provides a passagewayfor the light from the light source 4 to pass towards interface 1a, anda second through hole 7 provides a passageway for the reflected lightfrom interface 1b to pass towards the photosensitive element 5. Aparalleling lens 8 for reducing expansion in the light emitted from thelight source 4 is located in the through-hole 6. A protective material 9surrounds the base part 2 for preventing solution from entering theglass member 1 at its point of connection with the base part 2.

In FIG. 1B, which shows another embodiment of the present invention, atubular light-limiting limiting path member 10 is located in thethrough-hole 6 on the light source 4 side which is made of anon-transparent material as, for example, a synthetic resin or ceramic.This member 10 has a diameter somewhat smaller than that of thethrough-hole 6 and it includes a fine hole along its axis.

In operation, either of the instruments shown in FIGS. 1A or 1B areabout half dipped in a solution 11 to be examined. The light L radiatedfrom the light source 4 will pass through the transparent member toreach the incident light interface 1a at an incident light angle i andwill be divided. One divided light portion L₁ will be incident upon thesolution 11 to be examined. The other divided light portion L₂ will beinternally reflected within the transparent member 1. Further, the lightL₃ reflected by the reflector 3 will be directed back to thephotosensitive element 5. In case the incident light angle is close to90 degree, the light flux of the reflected light portion L₂ will berepresented by the following formula by the law of general lightreflection: ##EQU1## wherein

K is a constant determined by the incident angle i,

L_(V) is a total light flux radiated from the light source,

n_(A) is a refractive index of the transparent member and

n_(B) is a refractive index of the solution to be examined.

FIG. 2 can be used to explain the general principle of the presentinvention. When a light L_(O) having an energy E_(O) is projected at anincident light angle i upon an interface C with a substance B having anoptical refractive index n_(B) through a substance A having an opticalrefractive index n_(A), the light L_(O) will be divided into a reflectedlight portion L₁ having a reflection angle i and a refracted lightportion L₂ having a refraction angle r. As a result of theoreticalconsiderations, it is found that if the respective energies are E₁ andE₂, the relation of the following formulas will be established: ##EQU2##

By the above formulas, if i is constant, E₁ will vary with only therefraction angle r by the substance B. Theoretically this means that therefractive index of the substance B can be found by measuring the energyE₂ at a photosensitive point at which a non-divergent straight-linedfinely throttled beam-shaped light is arranged symmetrically with thenormal.

Now, in case an optical glass of a refractive index of 1.512 is used forthe transparent member and sulfuric acid solution having differingspecific gravities is used for the solution to be examined, the incidentlight angle based on the critical angle calculation will be as follows:

                  TABLE 1                                                         ______________________________________                                        Curve        A        B        C      C                                       ______________________________________                                        Incident light                                                                             61.60°                                                                          63.32°                                                                          64.71°                                                                        65.96°                           angle i                                                                       Specific gravity value                                                                     1.000    1.100    1.200  1.300                                   of sulfuric acid                                                              Refractive index                                                                           1.333    1.351    1.367  1.381                                   ______________________________________                                    

In the curves A, B, C and D, the incident light angle i is so determinedthat a total reflection may be made at each of the specific gravityvalues of 1.000, 1.100, 1.200 and 1.300.

One curve A will now be described in detail. When an optical instrumentof the present invention in which the incident light angle i has anincident light interface of 61.60 degrees is used, if variousmeasurements are made by varying the specific gravity of the sulfuricacid, at a specific gravity of 1.000 the reflected light flux will bemaximum in the total reflection. If this is given a value of 100, thereflected light flux will reduce to 25 at a specific gravity of 1.100and to 10 at a specific gravity of 1.200. That is to say, with anincrease in the specific gravity value, the reflected light flux willdecrease. The curve A in FIG. 3 shows this relation. The curves B, C andD are obtained in the same manner as curve A and show the samerelations.

FIG. 4 is an explanatory view showing the principle of U.S. Pat. No.3,977,790 to Schweizer et al. As described above, in the above U.S.patent a total reflection phenomenon of a light on an interface isutilized by using a divergent ray. That is to say, a light coming out ofa light source 21 will become a light having an expansion from L₁ to L₃when passing through a slit 22, it will pass through a transparentmember A and it will enter an interface C with a substance B to bemeasured. There, the light will become a light having light fluxes ofreflected lights L'₁ and L'₃, which will be received on a photosensitivesurface 23 and will be transmitted as an electric signal. It is wellknown that, in such case, the incident light angle i of the interface Cwith the normal can be made to make a total reflection by properlyselecting the transparent member A and the optical refractive indexesn_(A) and n_(B) of the substance to be examined. In such case, theincident light angle is called a total reflection angle or criticalangle and is represented by the following formula:

    i.sub.θ =(n.sub.B /n.sub.A)

where i.sub.θ is a critical angle and n_(A) >n_(B).

FIG. 4 shows the manner in which the optical refractive index of thesubstance to be examined varies from n_(B1) to n_(B3) and thereby thecritical angle varies from i.sub.θ1 to i.sub.θ3. In case n_(B) is of anintermediate value n_(B2), the light between the critical anglesi.sub.θ2 and i.sub.θ3 will be reflected by the total reflection but theother lights than it will be absorbed into the substance B as refractedlights and will not be projected on the photosensitive surface 23. Thehatched portion means a light flux not projected. At the time of n_(B3),the light flux will be of a minimum value and, at the time of n_(B1),the light flux will show a maximum value. It is the measuring principleof the above-mentioned U.S. patent to measure the optical refractiveindex of n_(B) by measuring the width of this projected light flux.Therefore, it is required that the light projected on the interfaceshould have an expansion width large enough to cover at least theabovedescribed critical angle variation range. By the way, as thespecific gravity variation range in a sulfuric acid lead battery isabout 1,000 to 1,320, the projected light flux must have a criticalangle width of at least 61 to 66 degrees (as calculated by using theglass member having a light refractive index of 1.516 as a transparentmember).

In the present invention, in order to elevate the measuring precision,it is preferable to make the light from the light source a beam light,that is, a non-divergent straight-lined ray as much as possible. Thus,the light from a general light-emitting diode having an expansion widthof about 10 degrees is reduced to an expansion of 0.5 degree by theparalleling lens 8 in FIG. 1A. Alternately, as shown in FIG. 1B, theexpansion component of the light can be reduced by passing the light fora fixed distance through a pinhole or a slit extending through thelight-emitting path member 10. The following formula is shown by apassing distance L and pinhole diameter d of the light-emitting path inmember 10:

    tan θ=d/L

In case d/L=0.1, θ=5.7°.

In case d/L=0.02, θ=1.14.

The light passing through such light-limiting path will be considerablyreduced in its expansion.

When experimentally confirmed, in the case of the parallelization byusing a convex lens of a diameter of 5 mm and focal length of 20 mm, theexpansion width is reduced to 0.5 degree without reducing the effectivelight flux. Further, in the case of a lens of a diameter of 5 mm andfocal length of 12 mm, the expansion width was 0.8 degree. Theparallelism was further improved by using semiconductor laser or gaslaser rays for the light source but there are defects in the size andprice. These are all confirmed to operate without trouble for themeasurement of the refractive index of the sulfuric acid electrolyte.Experimentally it is preferable that θ is not more than 1.5 degrees. Ifθ exceeds 1.5 degrees, the light expansion will become large and themeasuring precision will deteriorate. It is confirmed by experimentsthat if θ is not more than 1.5 degrees, the decomposability in the caseof measuring the specific gravity will be about 0.002, but at 2.5degrees it will be ±0.005 and at 4 degrees it will increase to about±0.014. In the case of utilizing a light-limiting path, L will be 2 to35 mm and d will be preferably in the above-mentioned θ range. By theway, the refractive index of the glass member is required to be above1.5. If it is not above 1.5, the measuring range will become narrow andthe precision will decrease. This requirement is important particular inthe measurement of the specific gravity of the electrolyte of sulfuricacid battery. The transparent member can be made of not only glass, butalso of a synthetic resin. However, a methacrylic resin will be attackedby sulfuric acid on the interface, which will influence the refractiveindex, and thus such a resin cannot be used. Vinyl chloride,polycarbonate and polyvinylidene chloride can be used as transparentmaterials, these being acid proof and at the same time displaying theabove-mentioned refractive index.

    ______________________________________                                                        Refractive                                                                    index    Transparency                                         ______________________________________                                        Vinyl chloride    1.54       70 to 90%                                        Polycarbonate     1.58       93 to 95%                                        Polyvinylidene chloride                                                                         1.60       50 to 70%                                        ______________________________________                                    

FIG. 5 shows another modification of the present invention. It ispositioned particularly into a lead acid battery and is adapted tomeasure the specific gravity of the electrolyte or to measure the chargeor discharge of the battery. It is fixedly connected with a base part102 made of a synthetic resin or the like. A reflector 103 is providedat the tip 101b of the transparent member 101 in the same manner as inthe device in FIG. 1. A light source 104 and photosensitive element 105are arranged in parallel with each other in the upper portion of thebase part 102. The base part is provided with through-holes 106 and 107.A paralleling lens 108 is arranged particularly within the through hole106 on the light source 104 side. This device body is fitted to anannular sleeve 109 which is screwed into a female screw 112 of the lidof the lead acid battery with a male screw 110 on the outer periphery ofthe annular sleeve 109. In operation, the tip of the transparent memberis dipped in the electrolyte 113 consisting of sulfuric acid of arequired specific gravity. A plate 114 of the lead acid battery iscontained together with the electrolyte 113 in a battery container 115.

Now, a light L radiated from the light source 104 will reach the firstincident light interface 101a and will be divided into a light portionL₁ entering the electrolyte 113 and a reflected portion L₂. This lightportion L₂ will be reflected by the reflector 103, will reach the secondincident light interface 101a' and will be divided into a light portionL₃ entering the electrolyte 113 and a reflected light portion L₄. Thelight portion L₄ will further reach the photosensitive element 5. Itslight flux is represented by the following formula: ##EQU3## wherein

i is an incident light angle on the incident light interface of thelight L and

r is a refraction angle in the electrolyte of L₁ and L₃.

As described above, the light flux of the light portion L₄ reaching thephotosensitive element 105 will vary correlatively with the specificgravity value of the sulfuric acid of the electrolyte 113.

Now, the relation between the specific gravity value of the sulfuricacid and the light current shown by the photosensitive element is asfollows:

                  TABLE 2                                                         ______________________________________                                        Specific gravity                                                              value of sulfuric                                                                          1.100   1.150   1.200 1.250 1.300                                acid                                                                          Light current (mA)                                                                         1.50    1.12    0.80  0.48  0.35                                 ______________________________________                                    

The above-described modification applying the optical instrument of thisembodiment to a lead acid battery has the following further advantages.

As the incident light interfaces of the transparent member are plural,the rate of reduction of the light reaching the photosensitive elementwill be large. As a result, any minute variation of the specific gravityof the sulfuric acid can be detected more easily. As the incident lightinterfaces are formed to be sloped, during the use of the lead acidbattery, generated oxygen and hydrogen gases will not be deposited onthe sloped incident light interfaces. As a result, gases will not bedeposited on the incident light interfaces, the light will not betemporarily disturbed and that the measured value will not be abnormal.However, as required, i.e., so that no gas may be deposited on theincident light interface, there may be provided either a shielding platebetween the plates or a cleaning means on the incident light interface.Further, it is well known that a lead acid battery will show a perfectdischarge when the specific gravity of the sulfuric acid of theelectrolyte is about 1.150 and a perfect charge at about 1.280. However,by a special using method, it may be expanded to be about 1.020 at theend of the discharge and about 1.320 at the end of the charge. In casethe optical instrument of the present invention is thus applied to alead acid battery, there will be able to be easily known the specificgravity value of the sulfuric acid from the above described reflectedlight flux and the charge or discharge through it. It is an inherentadvantage as applied to a lead acid battery.

FIG. 6 shows another modification of the present invention. An opticalinstrument is shown wherein a transparent member 201 and base 202 areconnected with a light source 204 and photosensitive element 205 throughrespective optical fiber cords 209 and 210 made of glass much to theadvantage of remotely measuring a solution. Its operation will be asfollows: A light L radiated from the light source 204 to the transparentmember 201 via a luminous optical fiber cord 209 and a paralleling tens208 will be reflected by a reflector 211, then it will reach an incidentlight interface 201a and then it will be divided into a light portion L₁entering the solution 211 to be examined and a reflected light portionL₂ reflected by the incident light interface 201a. The reflected lightportion L₂ will reach the photosensitive element 205 through theluminous optical fiber cord 210. The light flux of this reflected lightportion L₂ will be displayed by a meter or digits through an amplifier.Thus the specific gravity of the electrolyte and the charge or dischargeof the lead acid battery can be remotely measured. As a result, there isan inherent advantage that the maintenance of the lead acid battery iseasier.

FIG. 7 shows still another modification of the present invention. Alight L coming out of the light source 204 will pass through alight-limiting path 210 and will be reflected by the reflectiveinterface 201b of the transparent member 201. On the incident lightinterface 201a, a portion of the light L will advance as a light L₁ intothe electrolyte 211 and the other portion L₂ of the light L will bereflected and, will advance through the transparent member 201 and willbe received by the photosensitive element 205 in the base part 202. Inthis modification, the light from the light source will be reflected bythe reflective interface and then will be applied to the incident lightinterface. Therefore, the measurement can be made.

As further another modification, the light-limiting path may be broughtbefore the photosensitive element. However, in this manner, theeffective light flux will decrease.

It goes without saying that the optical instrument of the presentinvention can be used to not only measure the specific gravity of theacid in a lead acid battery but also to measure the characteristics ofother solutions as well, for example, to determination the concentrationof an aqueous solution of caustic soda or common salt, a petroleumdistillate or a transformer oil.

Other modifications of the present invention are also possible withoutdeparting from the spirit of the present invention. For example, thoughthe optical instrument of the present invention can be constructed so asto be fixed to the lead acid battery, it is not limited to thisconstruction but instead it can be constructed as a a portabletransparent member to be dipped by hand into an electrolyte in case itis only necessary to measure the electrolyte.

Further, it goes without saying that whether the light radiated from thelight source will reach the reflector through the incident lightinterface of the transparent member or will reach the incident lightinterface through the reflector can be freely selected and designed.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the spirit and scope of the invention as defined in theappended claims.

I claim:
 1. An optical instrument for measuring the specific gravity ofa solution, said instrument comprisingan elongated base body having afirst end and a second end, a light-emitting means located near saidfirst end of the elongated base body for emitting a ray of non-divergentlight through the elongated base body, a photosensitive element locatednear said first end of the elongated base body for sensing light passingthrough the elongated base body in parallel with said ray ofnondivergent light emitted by said light-emitting means, and atransparent glass member having a refractive index value of not lessthan 1.5 sealingly connected to said second end of the elongated basebody, said glass member including only two light-contacting surfaceswhich consist of (a) an incident light surface which is positioned andinclined such that said ray of non-divergent light emitted from saidlight-emitting means will strike the incident light surface and bedivided into a light portion entering the solution in which the opticalinstrument is partly immersed and a reflected portion, and (b) areflector surface; said reflector surface including a reflective coatingenabling 100% of the light hitting said reflector surface to beredirected towards said photosensitive element in a direction parallelto the ray of non-divergent light emitted from said light-emittingmeans.
 2. The optical instrument as claimed in claim 1, wherein saidelongated base member includes two parallel passageways therethrough,one for the passage of said ray of nondivergent light emitted from saidlight-emittting means towards said incident light surface and one forthe passage of the light reflected from said reflector surface towardssaid photosensitive element.
 3. The optical instrument as claimed inclaim 2, wherein a light ray-limiting means is positioned in thepassageway through which the ray of non-divergent light from saidlight-emitting means passes.
 4. The optical instrument as claimed inclaim 3, wherein said light ray-limiting means comprises a focusinglens.
 5. The optical instrument as claimed in claim 3, wherein saidlight ray-limiting means comprises a tubular member.
 6. The opticalinstrument as claimed in claim 3 wherein said light ray-limiting meanscontrols the divergence of the ray of light passing therethrough suchthat it has an expansion angle of not more than 1.5°, the opticalinstrument being thereby adapted to measure a specific weight of about1.000 to 1.320 of sulfuric acid.
 7. An optical instrument for measuringthe specific gravity of a solution, said instrument comprisinganelongated base body having a first end and a second end, alight-emitting means located near said first end of the elongated basebody for emitting a ray of nondivergent light through the elongated basebody, a photosensitive element located near said first end of theelongated base body for sensing light passing through the elongated basebody in parallel with said ray of non-divergent light emitted by saidlight-emitting means, and a transparent glass member having a refractiveindex value of not less than 1.5 sealingly connected to said second endof the elongated base body, said glass member including only twolight-contacting surfaces which consist of (a) a reflector surface whichis positioned and inclined such that said ray of non-divergent lightemitted from said light-emitting means will strike the reflectorsurface, and (b) an incident light surface positioned such that thelight reflected by said reflector surface will strike the incident lightsurface and be divided into a light portion entering the solution inwhich the optical instrument is partly immersed and a reflected portionwhich is directed towards said photosensitive element in parallel withthe ray of non-divergent light emitted from said lightemitting means;said reflector surface including a reflective coating enabling 100% ofthe light hitting said reflector surface to be redirected towards saidincident light surface.
 8. The optical instrument as claimed in claim 7,wherein said elongated base member includes two parallel passagewaystherethrough, one for the passage of said ray of nondivergent lightemitted from said light-emitting means towards said reflector surfaceand one for the passage of the light reflected from said incident lightsurface towards said photosensitive element.
 9. The optical instrumentas claimed in claim 8, wherein a light ray-limiting means is positionedin the passageway through which the ray of non-divergent light from saidlightemitting means passes.
 10. The optical instrument as claimed inclaim 9, wherein said light ray-limiting means comprises a focusinglens.
 11. The optical instrument as claimed in claim 9, wherein saidlight ray-limiting means comprises a tubular member.
 12. The opticalinstrument as claimed in claim 8 wherein said light ray-limiting meanscontrols the divergence of the ray of light passing therethrough suchthat it has an expansion angle of not more than 1.5°, the opticalinstrument being thereby adapted to measure a specific weight of about1.000 to 1.320 of sulfuric acid.